Glow-discharge tubes containing a radio-active primer



W. E- LOTHALLER Aug. 12, 1969 5 GLOW'DiSCHARGE TUBES CONTAINING ARADIOACTIVE-'PRIMER INVENTOR. WOLFGAN G E.LOTHALLER Filed June 26, 1967U i d States Patent: v

3,461,335 GLOW-DISCHARGE TUBES CONTAINING A RADIO-ACTIVE PRIMER WolfgangErich Lothaller, Leidschendam, Netherlands,

assignor, by mesne assignments, to US. Philips Corporation, New York,N.Y., a corporation of Delaware Filed June 26, 1967, Ser. No. 648,743Claims priority, application Netherlands, July 9, 1966, 6609664 Int. Cl.H013 17/20 U.S. Cl. 313226 5 Claims ABSTRACT OF THE DISCLOSURE Aglow-discharge tube employing a gas-filling consisting of a major amountof a first rare gas, a minor amount of a second heavier rare gas, and aradio-active primer.

The invention relates to a glow-discharge tube having a gas fillingconsisting of a rare gas, which tube also contains a quantity ofradio-active material for neutralizing the static delay in ignition.

In glow-discharge tubes without a priming electrode, the neutralizationof the static delay in ignition requires the use of a comparativelylarge quantity of radio-active material, i.e., up to 100 ,uC. Thisrequires stringent precautions to be taken during manufacture. Even useis made of a B-emitter so that no radio-active radiation is emittedoutside the tube. Safety measures made with regard to the fear forbreaking of the glass bulbs sometimes do not permit the use of apparatusin which large numbers of tubes are arranged. These regulationssometimes are so stringent that even the use of considerably smallerquantities of radio-active material exclusively for neutralizing thedelay in ignition of the discharge to that of a priming electrode inwhich a delay of 0.1 sec. is still permissible, is hardly possible.

In a glow-discharge tube having a gas filling consisting of a rare gasand moreover a quantity of radio-active material, according to theinvention, the gas filling also contains a small quantity of a heavierrare gas which with the principal gas does not produce a Penning eflectand does not form molecular ions with the main gas either.

Because the admixture with the principal gas does not produce a Penningeffect and that the quantity available is small, its influence not onlyon the ignition voltage but also on the burning voltage is very small sothat the admixture only results in a slight variation of the dischargeproperties of the glow-discharge tube.

The radio-active material forms not only ions of the principal gas, butalso ions of the admixture. The ions of the principal gas disappearrapidly by volume recombination of the molecular ions formed. The ionsof the principal gas may also transmit their charge to atoms of theadmixture. The ions formed of the admixture have such a lowconcentration that they cannot form molecular ions, and since theycannot form molecular ions either with the atoms of the principal gas, avolume recombination is not possible. As a result, the ions of theadmixture disappear only slowly so that their concentration iscomparatively high, even with a low intensity radio-active composition.The tube according to the invention consequently has the advantage thatthe strength of the radioactive composition required for neutralizingthe static delay in ignition can be considerably smaller than in theknown tubes.

A gas filling suitable for the use in accordance with the invention mayconsist of argon containing 0.1 to 1% of krypton.

The invention will be described more fully with reference to the drawingin which the sole figure is a partly developed perspective view of adischarge tube according to the invention.

In the figure, reference numeral 1 denotes a base of powdered glass and2 a glass envelope which terminates on the upper side in a sealing point3. Cathode 4 is secured by bulb-Welding to the end of a lead-in wire 5and the anode 6 to the end of a lead-in wire 7. Priming electrode 10 iswelded to the end of a lead-in wire 11 and ignition electrode 8 extendsas far as notch 12. in the cathode without projecting into the spacebetween the anode and the cathode. The priming electrode 10 extends asfar as in the notch 13 in the anode, also without projecting into thespace between the anode and the cathode. The cathode 4 is coated on therear side with a nickel coating 14. Because of symmetry, the anode 6also is provided on its rear side with a nickel coating 15. Otherwise,the electrodes consist of molybdenum plates.

vOn the base of the tube a dot of finely-divided titanium powder 17 isprovided in which tritium is absorbed. The strength of this radio-activecomposition is 0.1 c. The tube has a gas fillingat a pressure of 1000torr which consists of agron containing 0.5% of krypton.

After the pumping treatment, the surfaces of the electrodes are cleanedby sputtering so that a dark deposit 16 is formed on the wall of thetube. The tube of the construction described has an anode-cathodebreakdown voltage of more than 280 v. and an auxiliary anode ignitionvoltage of approximately 130 v. The operating voltage is v. and theoperating current is 3 ma. The current from the anode to the primingelectrode 10, required for preventing delays in ignition in the maindischarge path is 10 ,ua.

The influence of the krypton addition on the operating voltage and onthe ignition voltage is extremely small. Because of the krypton,however, the strength of the tritium composition can be considerablyreduced, while attaining a delay in ignition of only 0.1 sec. for thepriming discharge. In the absence of the krypton, this quantity wouldhave to be approximately 1 ,uc. in order to obtain the same delay inignition.

While the invention has been described with reference to a particularembodiment thereof, other modifications will be apparent to thoseskilled in this art without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

1. A glow-discharge tube comprising an envelope containing a pair ofelectrodes and an ionizable medium consisting essentially of a firstrare gas, and a small quantity of heavier rare gas which with the maingas does not produce a Penning effect and does not form molecular ionswith said main gas, and a quantity of radioactive material having astrength substantially less than that 3 required in the absence of saidheavier rare gas dispose within said envelope for reducing staticignition delay.

2. A glow-discharge tube as claimed in claim 1 in which the first raregas is argon and the heavier rare gas is krypton which is present in anamount of 0.1 to 1% by 5 volume.

3. A glow-discharge tube as claimed in claim 2 in which the radioactivematerial is tritium.

4. A glow-discharge tube as claimed in claim 3 in which the radioactivematerial has a strength of 0.1 o.

5. A glow discharge tube as claimed in claim 4 in which the tritium isabsorbed in titanium.

References Cited UNITED STATES PATENTS H M 1,481,422 1/1924 Holst et a1.313-226 2,629,842 2/1953 Townsend 313-224 X JAMES W. LAWRENCE, PrimaryExaminer RAYMOND F. HOSSFELD, Assistant Examiner U.S. Cl. X.R. 3l32l0,224

